The invention relates to a press fixing apparatus for the fixing of toner images, with three pressing rolls or rollers having axes disposed substantially in a common plane. The pressing rolls are laterally supported in lateral bearing blocks at their respective ends and are resiliently pressed against one another.
With a known construction of the above-mentioned kind (German published application--DE-AS No. 28 09 750) two pressing rollers forming a clamping slot are carried in lateral bearing blocks in a U-shaped frame, whereby one of the pressing rollers is slidably guided at its ends and is loaded with pressure springs in the direction toward the clamping slot. These resiliently pressed pressing rollers are supported at the diametrically opposite side of the other pressing rollers by means of a support roller, which support roller exhibits a shorter axial length and which is carried in a fixed bearing block at the U-shaped frame, whereby its bearings are pressed with further pressure springs against the middle pressing roller. With this press fixing apparatus there is achieved a resultant reduction in the construction space because the diameter of the pressing rollers can be made smaller. However, the design and manufacturing technology expenditures are relatively high for this construction.
The invention is based upon the problem to so build a press fixing apparatus of the above-mentioned kind that most simple construction is obtained along with a reduction of the necessary construction space. This problem is solved according to the invention in that a common bearing block is provided at each side, for the three pressing rollers which bearing blocks serve to support the bearings for the two outer pressing rollers with spring tension against respective bearing seats, also serve to accommodate a movable guide disposed in a common plane for the bearing of the middle pressing roller.
Through this construction the number of bearing blocks and, above all, also the number of the movable bearings is reduced, while furthermore the number of the elements is reduced which are necessary to facilitate the pressing force.
In especially advantageous embodiments of the invention it is provided that the bearing blocks are respective single part construction pieces which exhibit oppositely disposed somewhat half cylindrical bearing seats for the bearings of the outer pressing rollers, which bearing seats are connected together by means of frame sections or web portions which form a guide for the bearing of the middle pressing roller, whereby at each bearing block one of the frame portions is subdivided by means of a separating gap into two sections which are tensioned with respect to one another by means of at least one spring. This arrangement facilitates a very simple construction of the bearing blocks which is formed without joints and which requires only two springs to bring about the necessary pressing forces. Thereby, it is appropriate and practical if the separating gap or slot between the two sections of one of the frame portions extends into one of the bearing seats. It is also accomplished that an exact guidance is maintained during the relative movement inside of the separating slot. Practically, the frame portion containing the separating gap exhibits a larger cross section than does the undivided support frame portion.
In further embodiments of the invention it is provided that both lateral bearing blocks are connected with one another by means of cross members extending parallel to the axes of the outer pressing rollers. The cross members serve to accommodate the axial forces. It is advantageous if the cross members--as seen in the direction of the pressing rollers--are disposed in corners of a rectangular that surrounds the middle pressing roller. With this arrangement an especially advantageous force balancing relationship is achieved.
An especially simple assembly is achieved by providing the cross members with limit stops supported at the facing surfaces of the frame support portions of the two bearing blocks and with hook formed protrusions penetrating these frame support portions. Sliders are slidable into the respective hook-formed protrusions, which sliders then abut the oppositely disposed surfaces of the frame support portions of the bearing blocks. In this manner the assembly of the press fixing apparatus as a construction unit is achieved without requiring the use of screws, bolts, or the like.
It is especially advantageous if the protrusions of the cross members exhibit a somewhat triangular shaped cross section in the region extending through the bearing blocks, the sides of which are supported at the surface of the frame members, the outer surfaces of the bearings of the outer pressing rollers and the slide. In this manner the cross members are exactly positioned and furthermore the advantage is achieved that through the level of the slider a positioning of the pressing rollers is achieved so that they can, in this manner, be adjusted so that their cover surfaces are not disturbed or are only lightly disturbed during running without paper.
These and further objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.